Shroud fastening for turbine blades



May 20, 1941. R. P. KROON SHROUD FASTENING FOR TURBINE BLADES Filed March 23, 1959 INVENTOR REmou'r F. KRooN.

' WITNESSES:

Q, W W ATTORNEY when M WWW/m Patented May 20, 1941 SHROUD FASTENING FOR TURBINE BLADES Rcinout P. Kroon,

Swarthmore, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 23, 1939, Serial No. 263,617

4 Claims.

My invention relates to a turbine blade fastening, more particularly toshrouding of the integral, highly-stressed type, and it has for an object to provide a shroud connecting the blades together in a simple fashion and producing a strong fastening.

In the provision of highly-stressed shrouding for turbine blades, it is advantageous to form the shrouding integral with the outer ends of the blades, and this can best be accomplished by having each blade formed with an outer integral shroud element, the shroud elements being connected in end-to-end relation to form a complete shroud. In order that the strength of the shroud may be preserved, the location and kind of connections is important. It has heretofore been proposed to Weld the shroud elements together in end-to-end relation, but this has en-' tailed the difiiculty of excessive contraction of the welds. In accordance with the present invention, the abutment joint is located so as to be subject to small or zero bending moments and the welds are so arranged that they are not only spaced from the most vulnerable points, where the shroud elements join the blade section, thereby resulting in as little damage as possible at these but drawing of the weld and consequent stresses set up in the blades and shrouds are reduced by the use of localized weld deposits instead of a relatively large or a long weld for each joint, this result being even better achieved by having the deposits made as small as possible for adequate strength, this reduction being possible on account of low or zero bending moment, and by the proper use of shims between the shroud joints.

Another object of the invention is the provision of turbine blades or vanes having integral shroud pieces united in end-to-end relation, the joints between adjacent shroud pieces being disposed in planes where the bending moment in the shroud is small.

A further object of the invention is the provision of blades having integral shroud pieces united in end-to-end relation by weld material disposed at points spaced from the median points of the convex surfaces and from the concave face edges.

These and other objects are elTected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawing forming a part of this application, in which:

Fig. 1 is a side elevational view, a portion points on account of welding,

thereof being broken away along the line I-I of Fig. 2, showing a portion of a row of the turbine blading in section; I

Fig. 2 is a plan view of the structure shown in Fig. 1; and,

Fig. 3 is an enlarged fragmentary view of the sectioned portion of Fig. 1, together with a stress diagram of the bending moments for the fragmentary section shown.

In the drawing, there is shown, at It], a blademounting element, such as a turbine rotor, on which are supported a row of blades ll, each blade having at its outer, or free end, an integral spacing piece or shroud element I 2.

Preferably, the spacing pieces or shoud elements are concentric with respect to the blade section and project beyond the latter slightly in both directions circumferentially. The edges of the adjacent spacing pieces provide joints l3 so positioned with respect to the blade section as to coincide at least approximately with the point of minimum bending moment. (See Fig. 3.)

It is, therefore, desirable to locate the joints between adjacent spacing pieces at, or close to, the regions of low or zero bending moment (m m, Fig. 3) of the shroud strip, these regions being easily located inasmuch as they lie midway of the regions of maximum bending moment (12 n, Fig. 3), the latter passing approximately through the neutral axes of the blades.

It has also heretofore been proposed to weld together the abutting shroud element edges by means of, welds extending for substantially the full width of the shroud; however, this type of weld involves large contractions resulting in high stresses in the blades and the shroud. There-- fore, since the joints are to be arranged at points of low or zero bending moment, the requirement for strength on the part of the weld is reduced, in consequence of which the weld connections may be constituted by relatively small weld deposits. By having relatively small weld deposits, it is possible to locate them so as to be as far away as possible from the most vulnerable points where the blade and shroud elements join, with the result that the structure is damaged at these points as little as possible on account of welding. Furthermore, by the use of relatively small weld deposits, drawing or contraction stresses set up in the blades and the shrouds can be minimized, particularly by making the weld as small as possible for adequate strength and by the proper use of shims between the shroud joints.

Means are provided for integrally uniting the ber, a row of blades spacing pieces l2 in end-to-end relation to form the shroud strip for the row of blades ll. Cuplike recesses M are formed at the joints l3 in spaced relation, and are filled with weld metal [5 to autogenously connect the spacing pieces l2.

Preferably, the cup welds are spaced as far as possible from points :0 on-convex blade face median radial lines and points y at concave face edges, these being the most vulnerable points where the blade and shroud elements join, and the spacing of the weld deposits from these points assures that damage of the blading on account of welding will be minimized. 7

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. In combination with a blade-mounting memmounted on said member; a shroud element integral with the outer end of each blade and the shroud elements abutting to form a shroud strip; each pair of adjacent shroud elements having the joint formed by their abutting edges lying in a region of low or zero bending moment of the'shroud strip; said abutting elements of each joint having a pair of spaced cup spaces extending from the outer surface of the shroud inwardly for a portion of the thickness of the latter andformed by complemental concavities in adjacent abutting edges of the shroud elements, said cup spaces of each pair being spaced to either side of the center of its joint and being spaced from the convex back and the front edges of the blade sections; and weld deposits filling the cup spaces and autogenously connect ing abutting shroud elements.

2. In combination with a blade-mounting member; a row of blades mounted on said member; a shroud element integral with the outer end of each blade and the shroud elements abutting to form a shroud; each pair of adjacent shroud elements having the joint formed by their abutting edges lying in an axial plane substantially midway of axial planes passing through the neutral axes of the blades of said pair, whereby the joint is subject to low or zero bending moment values; said abutting elements of each joint-having a pair of spaced cup spaces extending from the outer surface of the shroud and inwardly for a portion of the thickness of the latter and formed by complemental concavities in adjacent abutting edges of the shroud elements; said cup spaces being arranged substantially midway between the convex back of the section of the leading blade of the pair and the front edges of the section of the following blade; and weld deposits filling the cup spaces and autogenously connecting abutting elements of such joint.

3. In combination with a blade-mounting member; a row of blades mounted on said member; a shroud element integral with the outer end of each blade and the shroud elements abutting to form a shroud; each pair of adjacent shroud elements having the joint formed by their abutting edges lying in an axial plane substantially midway of axial planes containing the neutral axes of the blades of said pair, whereby the joint is subject to low or zero bending moment values; said abutting elements of each joint having a pair of spaced cup spaces extending from the outer surface of the shroud and inwardly for a portion of the thickness of the latter and formed by complemental concavities in adjacent abutting edges of the shroud elements; said cup spaces being spaced to either side of the median plane of rotation of the blades to provide for spacing thereof from the median radial lines of the blade convex faces and from the edges of the blade concave faces; and weld deposits filling the cup spaces and autogenously connecting the elements of each joint.

4. In combination with a blade-mounting member; a row of symmetrical blades mounted on said member; a shroud element integral with the outer end of each blade and the elements abutting to form a shroud; each shroud element extending circumferentially from the concave and convex faces of its blade so that the joints formed by abutting shroud elements are arranged in axial planes and overlie the blade passages with each joint located, in relation to the passage which it overlies, between a plane including the edges of the concave forward face of the passage and a tangent plane including the median radial line of the convex rearward face of the passage; said abutting elements of each joint having a pair of spaced cup spaces extending from the outer surfaces of the shroud and radially inward for a portion of the thickness of the latter and formed by complemental concavities in abutting edges of the shroud elements; said cup spaces of each joint, in relation to the blade passage which it overlies, being arranged substantially midway between the radial medium line of the convex face of the passage and each concave face edge; and weld metal filling the cup spaces and autogenously connecting the abutting edges of the joints.

REINOUT P. KROON. 

